Field of the Invention
The present invention relates to an art of a vapor chamber that diffuses heat conducted to one of an upper plate or a bottom plate of a hollow flat container to the other plate in the form of a latent heat of a fluid encapsulated in the container.
Discussion of the Related Art
A heat pipe has been widely used in the conventional art to remove heat from a cooling object in the form of latent heat of working fluid. JP-A-11-195738 describes a flat heat pipe in which a hollow flat container is comprised of a rectangular upper plate and a cup-shaped main body. An inner surface of the container is covered entirely with a porous wick, and a condensable working fluid is encapsulated therein while evacuating non-condensable gas. According to the teachings of JP-A-11-195738, the flat heat pipe thus structured is enclosed entirely by a base of a heat sink but except for a bottom plate, and a CPU to be cooled is contacted to the bottom plate.
JP-A-2000-161879 also describes a flat heat pipe in which an inner surface of a hollow flat container is covered entirely with a wick formed of a sintered copper particle. In order to enlarge an evaporating area, a plurality of protrusions also formed of the sintered copper particle are juxtaposed on the wick. Heights of sidewalls of the container are higher than those of the protrusions, and a bottom of a heat sink is contacted to an upper plate of the container to exchange heat therebetween.
JP-A-2004-238672 also describes a flat heat pipe in which a wick made of sintered copper powder is attached individually to each inner face of an upper lid and a bottom plate of a hollow flat container, and those wicks are connected through a plurality of columns also made of sintered copper powder.
According to the teachings of JP-A-11-195738 and JP-A-2000-161879, the inner surface of the container is covered entirely with the porous wick. In turn, according to the teachings of JP-A-2004-238672, the porous wicks are formed on both upper and bottom inner surfaces of the container, and those wicks are connected by the columns. According to any of the teachings of the foregoing prior art documents, the condensed working fluid is returned to the evaporating portion by capillary pumping of the porous wick. However, a fluid flow resistance of the porous wick also covering a portion other than the evaporating portion is rather high. That is, the working fluid in the liquid phase is held at the portion other than the evaporating portion. In the heat pipes thus structured, if the working fluid is heated excessively at the evaporating portion, the working fluid may be evaporated more than necessary. Consequently, the evaporating portion would be dried-out thereby reducing a heat transfer capacity. According to the teaching of JP-A-2004-238672, heat transfer capacity may be enhanced by transportation heat not only by the working fluid but also through the columns. However, the column taught by JP-A-2004-238672 is also constructed of sintered porous material and the heat resistance among particles forming the columns is rather high. Therefore, the heat transfer capacity of the heat pipe taught by JP-A-2004-238672 may not be enhanced and dry-out of the evaporating portion may be caused.
The present invention has been conceived noting the foregoing technical problems, and it is therefore an object of the present invention is to provide a vapor chamber having improved heat transfer capacity by efficiently returning the working fluid to the evaporating portion.